In this passage Winston is in the dreaded 'Room 101' with O'Brien and is forced to confront his worst fear in the world, rats. He succumbs to the pressure and commits the ultimate act of betrayal, the betrayal of Julia, to avoid this horror. This is a turning point for Winston because from this point on he is susceptible to the Party's influence; the author manages to emphasize this through several narrative devices.
This passage consists mostly of direct speech interrupted by short passages of free indirect discourse from Winston's point of view. This is a contrast to the lead up to this extract which contains mostly free indirect discourse with a small amount of direct speech. The effect created by this change is a reinforcement of the change in location, previously he was in a reasonably comfortable cell, however, with this change to direct speech he is now in a different cell.
Another effect created by the direct speech is a personal connection between O' Brien and Winston, the former taking immense personal pride in the work that he does. The change here also represents the change about to occur in Winston as he becomes another robot-like figure.
This passage differs from the rest of the booking in a number of ways. The tone of Orwell's writing voice is a fairly unassuming one, explicitly stating things throughout the novel using a casual tone as opposed to a formal one; however, here he does not break off to mock things. This change represents the turning point for Winston emphasizing the seriousness and gravity of the situation.
At the beginning of this passage Orwell uses short sentences and short paragraphs which build up the tension:
'The door opened again. A guard came in, carrying something made of wire, a box or...